1. Field of the Invention
This invention relates to ship unloading apparatus and more particularly to belt feeder gates for discharging bulk material such as iron ore pellets, crushed stone, coal or the like from a ship hold onto an unloading conveyor belt beneath the ship hold.
2. Description of the Prior Art
In the prior art relating to unloading bulk material from the hold of a self-unloading ship having a hoppered bottom it has been customary to provide gates underlying the hopper openings at the lower end of the ship hold, which gates have been selectively openable to permit dispensing of bulk material from the open lower end of a given hopper onto an underlying conveyor belt which carries the bulk material thus unloaded to a suitable discharge point of the conveyor system, the underlying conveyor belt usually moving in a lengthwise direction relative to the longitudinal axis of the ship. The gates in the prior art positioned in underlying relation to the hopper bottoms have generally been movable in a direction parallel to or lengthwise of the conveyor belt as shown, for example, by U.S. Pat. Nos. 2,505,982 issued to John F. Meissner on May 2, 1950 and 3,191,998 issued to Charles L. Howlett on June 29, 1965. However, broadly speaking, it is also known in the prior art to provide in a ship unloading arrangement belt feeder gates positioned in underlying relation to the hopper opening and movable in a lateral direction relative to the direction of movement of the underlying belt, such arrangement being shown by U.S. Pat. Nos. 842,338, issued to Charles D. Ross on Jan. 29, 1907, and 1,756,518 issued to Levy McMillan on Apr. 29, 1930.
The use of hopper gates which move in a direction transversely or laterally of the direction of movement of the conveyor belt is preferable since it permits the laterally movable gate to be retracted to a position in underlying relation to the exterior surface of the laterally inclined walls of the associated overlying hopper where the laterally retracted gate is in completely noninterfering relation to the discharge gates of longitudinally contiguous hoppers. In contrast, where hopper discharge gates which move in a direction lengthwise of the unloading conveyor are used as in the aforementioned Meissner and Howlett patents, the longitudinal opening movement of a given hopper gate must be limited to prevent interference with the gates of longitudinally contiguous discharge hoppers.
The net result of this distinction between hopper discharge gates which move laterally of the underlying conveyor as compared to hopper gates which move longitudinally of the underlying belt conveyor is that hoppers having larger discharge openings or bottom mouths can be used with gates which move in a lateral direction relative to the direction of movement of the conveyor then can be used with gates which move in a direction parallel to the longitudinal movement of the conveyor.
A further advantage of hopper discharge gates which move in a lateral direction relative to the direction of movement of the underlying conveyor belt is that the operating mechanism for effecting opening and closing movement of the discharge gates can be located in what is known in the art as the "hog ridge" which is the inverted V-shaped hollow space defined beneath two upwardly converging oppositely longitudinally inclined walls of two longitudinally adjacent discharge hoppers. This feature just mentioned is shown per se by the aforementioned U.S. Pat. No. 1,756,518 issued to Levy McMillan.
In effectuating the opening and closing movement of the discharge gates of the hopper it is desirable that the gate be provided with wheels which move on tracks, which feature is broadly shown by the aforementioned United States patents to Meissner and Howlett, although as previously mentioned in the patents to Meissner and Howlett, the gate members are movable in a direction parallel to the lengthwise direction of travel of the underlying conveyor belts. An important feature of the present invention is the provision of a hopper discharge gate whose wheels are so constructed with relation to the tracks on which they run as to prevent any "play" or wobble of the wheels relative to the tracks, thereby insuring that the wheeled gate moves in a substantially constant and undeviating linear path of movement whereby to provide a constant and stabilized relation of the path of movement of the wheeled gate relative to the power means which imparts movement to the gate such as a hydraulic ram, for example. This feature does not appear to be shown by any of the aforementioned patents.